Protractor.



PATENTED AUG. 8, 1905.

A. E. ENBERG. PROTRACTOR.

APPLICATION FILED JAN.8,1904.

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UNITED STATES PATENT OFFICE.

PROTRACTOR.

Specification of Letters Patent.

Patented Aug. 8, 1905.

Application filed Iauuary 8, 1904. Serial No. 188,159.

To all whom it may concern:

Be it known that I, AxnL EDWIN EN'BERG, a citizen of the United States, residing at Worcester, in the county of W'orcester and Commonwealth of Massachusetts, have invented a new and useful Improvement in Protractors, of which the following is a specification, accompanied by drawings forming a part of the same, in which Figure 1 is a plan view of a draftsmans triangle containing a protractor embodying my invention. Fig. 2 is an edge view of the same. Fig. 3 is a sectional view on line 3 3, Fig. 1. Fig. 4 is an edge view of the bar of the protractor detached from the triangle.

Similar reference-figures refer to similar parts in the difi erent views.

The object of my invention is to provide a protractor capable of being combined with other drawing instruments, such as a triangle, although it is possible to embody my protractor with other similar drawing-tools, and I do not, therefore, confine myself to its use with a triangle. It is only necessary that the combined instrument should be in the form of a thin plate like that forming a draftsmans triangle.

In the accompanying drawings, representing a draftsmans triangle having my improved protractor embodied therein, 1 denotes the triangle, which may be made from celluloid, rubber, or other suitable material.

2 is a central opening in the triangle in approximately the shape of a sector of a circle having sides 3 3 with a circular recess 4 at the converging ends of the sides 3 3 and an are 5, forming the third side of the opening 2, said circular recess being concentric with the are 5. The are 5 is suitably graduated and is provided with a V-shaped groove 6, and the edge of the circular recess 4 is provided with a similar V-shaped groove 7.

Held within the opening 2 is a protractorbar 8, having its opposite ends provided with V-shaped edges 9 9, adapted to fit the V-shaped grooves 6 7. One end of the protractor-bar is curved to fit the curved are 5, and the opposite end is provided with a tailpiece 10, curved to fit the circular recess 4. The tailpiece 10 is bent in semicircular form and is slightly elastic, so that when the bar 8 is crowded into position, as shown in Fig. 1, the tailpiece 10 will exert a slight pressure in the direction of the length of the bar, so as to hold the V-shaped edges of the bar in close engagement with the V-shaped grooves in the edges of the triangle, and in order to accomplish this result the combined length of the bar 8 and tailpiece 10 is slightly more than the distance between the edges of the are 5 and the circular recess 4, so that the tailpiece 10 s slightly compressed when the bar is placed in position, so that the pressure of the tailpiece 10 against the abutting edge of the triangle will serve to hold the bar in position and also to produce sufficient friction between the ends of the bar and the edges of the triangle to enable the bar to be held in any of its adjusted positions within the opening 2. The edge 11 of the bar is drawn on a radial line of the curved arc 5 and extends a short distance past the center 12 of the circle of which the line 5 is an arc.

A recess 13 is formed in the upper surface of the bar 8 to enable the bar to be swung around an axis corresponding with the center 12 of the circular arc 5 and placed in any desired position within the opening 2, as indi cated by the graduated are 5, one of such positions being indicated by broken lines 14.

In the drawings I have shown an extension 15 upon one side of the bar 8, on which other graduations may be placed to form a micrometer-gage. if desired; but this is not essential to my invention.

What I claim as my invention, and desire to secure by Letters Patent, is

1. The within-described protractor consisting of a plate having an opening in the shape of a sector of a circle and a protractorbar, of approximately the same thickness as the plate, rotatably held in the apex of the sector and in the same plane as the plate.

2. The combination with a plate provided with an opening in the shape of a sector of a circle, said opening having a curved recess at the apex of the sector, said curved recess being concentric with the sector, of a protractorbar having one of its ends rotatably held in said curved recess and being in the same plane as the plate.

3. The combination with a plate having an opening in the shape of a sector of a circle, the protractor-bar in order to hold the oppoand having the curved side of said opening site end of the bar in contact With the curved graduated, with a curved recess in the apex side of the opening.

of said opening, said recess being concentric with the sector, a protractor-bar having a curved elastic tailpiece adapted to be compressed in said curved recess, whereby its elasticity Will exert a longitudinal strain upon AXEL EDWIN ENBERG.

Witnesses:

RUFUS B. FOWLER, PENELOPE COMBERBACH. 

